Method of moulding electron tubes around removable mandrels carrying the tube electrodes



Dec. 24, 1968 R KELLEY 3,417,448

METHOD OF MOULDING ELECTRON TUBES AROUND REMOVABLE MANDRELS CARRYING THE TUBE ELECTRODES Filed May 24, 1966 50 z 5g INVENTOR. 5 2. 54 641 6! 4245 United States Patent 0 METHOD OF MUULDING ELECTRON TUBES AROUND REMOVABLE MANDRELS CARRY- ING THE TUBE ELECTRODES Ray H. Kelley, Los Angeles, Calif., assignor to Ray H. Kelley & Associates, Santa Monica, Calif., a partnership Filed May 24, 1966, Ser. No. 552,492 14 Claims. (Cl. 29-2513) generating, accelerating and scanning an electron beam.

The gun structure consists of many distinct elements or electrodes spaced apart on several slender metallic and ceramic rods. A rigid structural support for the electrodes is provided only when the tube is positioned with these slender rods vertical. However, usually such tubes are positioned such that the rods lie in a horizontal plane. When arranged in this manner, the support rods provide only a cantilever support and have only the resistance to bending provided by the section moduli of the very small diameter rods, typically about three onehundredths of an inch in diameter. Thus, it will be apparent that for a large number of the typical applications of cathode ray tubes, and other tubes for that matter, the various electrodes thereof are not rigidly supported thereby giving rise to positional variations from I;

one electrode to another. As a result, problems are encountered with respect to the proper modulation, focus and deflection of the generated electron beam, necessitating the use of elaborate control circuitry which is provided with adjustable elements to enable compensation for physical changes within the gun structure. Furthermore, the large diameter, typically one-half inch or greater, of the individual elements in the gun and their close proximity create relatively large capacitances with which the control circuit designer must laboriously cope. Additionally, because of the cantilevered structure of the gun elements and the numerous parts from which the electrodes and supporting structure thereof are constructed, it is extremely difficult to miniaturize the gun structure for enabling the practical manufacture or relatively tiny tubes.

Accordingly, it is an object of the present invention to provide an improved method for constructing electron tubes.

It is an additional object of this invention to provide a method for constructing electron tubes without the necessity of cantilevered supporting members.

A further object of this invention is the provision of a method for constructing electron tubes, such as cathode ray tubes, in a relatively simple manner which enables the manufacture of relatively small tubes.

An additional object of this invention is to provide an improved construction for an electron tube.

Another object of the present invention is to provide an electron tube construction wherein the various electrodes thereof are supported by a portion of the tube itself.

A still further object of this invention is to provide an electron tube construction, such as a cathode ray tube, wherein the electrodes thereof are supported by a portion of the tube itself without the requirement of individual supporting members therefor.

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These and other objects of this invention will become more apparent upon a consideration of the following description taken in conjunction with the drawing in which:

FIGURES 1A and 1B generally illustrate an electron tube constructed in accordance with the teachings of the present invention;

FIGURE 2 is an enlarged view of a portion of an electron tube constructed according to this invention;

FIGURES 3A and 3B are cross-sectional views illustrating the manner in which the electrodes are secured within an electron tube;

FIGURES 4 through 8 illustrate the manner in which typical electrodes are formed.

According to an exemplary embodiment of the teachings of the present invention, the electron elements of a tube, such as a cathode ray tube, are supported by the tube envelope rather than by individual supporting ele ments. For example, the various electrodes are plated on forms, the plated forms are positioned on a mandrel within a mold, and the envelope material, such as glass, is poured into the mold. The mandrel is removed, and the forms are dissolved by a suitable solution, leaving only the plated electrodes permanently secured to and supported by the envelope. Leads to the electrodes are either plated thereon during the plating of the electrode itself or attached after plating. After removal of the forms, the leads may be coupled with base pins in a conventional manner, and in the case of a cathode ray tube a face plate may be bonded to the envelope. The envelope then serves to rigidly support and precisely maintain the electrodes in position without the requirement of individual supporting elements.

The electrodes of electron tubes as discussed above are rigidly supported and remain in their precise positions without sagging as a result of tube orientation. Distributed capacitances can be substantially reduced in small tubes, and the stray capacitances occasioned by the usual metallic supporting elements are eliminated thereby simplifying the capacitance problems with which control circuit designers rnust cope. This construction also provides more consistent high production performance enabling consistent quality tubes to be produced, which in turn enables a reduction in variable operational controls and circuits therefor. Hand assembly is substantially reduced, as well as the volume of electrode material required, thereby resulting in lower production costs. Furthermore, the porosity of the plated electrodes can be held down and this, along with the reduced electrode volume, results in less out-gassing of electrode elements thereby requiring less gettering in the completed tube and aids in assuring increased operational life.

Turning now to the drawings, FIGURES 1A and 1B respectively illustrate side and rear views of a miniature cathode ray tube which may be constructed according to the teachings of this invention. Although reference will be made to cathode ray tubes in describing exemplary embodiments of the present invention, it should be understood that the concepts herein are applicable to the generic family of electron beam tubes, including such tubes as cathode rays tubes, television black and white and color picture tubes, storage tubes, vidicon tubes, iconoscope tubes, photomultiplier tubes, etc., which require a plurality of precisely spaced electrodes, The tube illustrated in FIGURES 1A and 1B may have a typical size of approximately two and one half inches by one and three fourths inches, and have a neck diameter of approximately one half inch. The tube includes an envelope 10, face plate 11 and neck 12. The neck includes the various electrodes comprising the gun of the tube, and leads from the electrodes terminate in pins 14 in a base 15. The envelope 10, face plate 11 and base 15 may be of conventional materials. For example, the envelope 10 and face plate 11 3 may be of glass or other suitable material, and the base 15 may be formed of glass or a suitable plastic.

FIGURE 2 illustrates the tube neck, gun structure and base in greater detail. The neck 12 typically is formed of glass, but ceramic or other plastic materials may be used. As will be discussed subsequently, the various electrodes of the gun structure are held in place within a mold and the envelope and neck are poured or otherwise molded around the electrodes. The gun structure includes a heater 20, which is added after the neck and envelope are molded and the electrode forms are removed, to heat a cathode 21. The heater 20 is shown merely as a cylinder attached to the base and not in detail, but may comprise a conven tional wound filament or may be a ferrite type heater. An electrode 22, which may be termed the first grid, is arranged about the cathode 21, and is followed by electrodes 23 through 25 which respectively may be termed the first anode, second grid and second anode. As will appear subsequently, each of these electrodes is formed by plating a thin layer of a suitable metal on a mandrel, with the neck material being formed about the electrodes to rigidly secure them in place, followed by removal of the mandrels. Leads for the electrodes may be formed during the plating process or may be attached to the electrodes after plating. Thus, a lead 30 is shown coupled between the electrode 22 and a base pin 31, a lead 32 is coupled between the electrode 24 and a base pin 33, and leads 34 and 35 coupled with respective electrodes 23 and 25 are connected through a lead 36 to a pin 37. The lead 36 may extend into the void within the completed envelope at 38 to enable an internal ground to be provide. A lead 39 is provided for the cathode 21 and connected to a bore pin but are not seen in FIGURE 2 (note FIGURE 3B shows lead 39), and the heater 20 has a pair of leads connected to respective base pins, only one lead 40 and pin 42 being seen in FIGURE 2. The base is secured to the neck 12 by an adhesive, epoxy resin, or the like 43.

FIGURES 3A and 3B illustrate the manner in which the neck and gun structure of a tube, such as a cathode ray tube, are formed, and FIGURES 4 through 8 illustrate the manner in which the electrodes themselves are plated prior to the forming of the gun structure. Briefly, each of the electrodes is plated on a mandrel positioned on a form, and the mandrel with the plated electrode is removed from the form and poistioned within a mold 50. The mold 50 typically is made of tool steel, and has a cylindrical cavity 51 therein for forming the neck and gun structure, the cylindrical cavity terminating in a conical opening 52 for forming the envelope portion of the tube between the neck and face plate. The mold 50 is inclined at 53 to aid in coupling the base to the neck of the tube. A projection 54, which typically is cylindrical, extends into the cylindrical cavity 51 to leave a cavity into which the heater of the tube is inserted prior to at taching the base.

The cathode 21 which in the shape of a cylindrical cup is formed by plating electrode material onto a mandrel 60 as shown in FIGURE 4. The mandrel 60 is precisely shaped to provide the desired electrode, and is made of a material which can be suitably dissolved after the neck and gun structure are molded. For example, the mandrel 60 may be made of aluminum which can be easily machined to fine manufacturing tolerances. The mandrel 60 is positioned on a suitable form 61 which may be made of an acrylic plastic, such as that sold under the trade name Lucite, or other suitable material. The form 61 provides a support, and also the base thereof serves as a buffer to ensure that only the exterior of the mandrel 60 is plated.

In manufacturing a relatively small tube such as that shown in FIGURES 1A and 1B, the diameter of the mandrel 60 may be approximately 0.105 inch, have a thickness of approximately 0.010 inch, and be approximately 0.115 inch long. The cathode 21 may be formed by electroplating nickel on the mandrel 60, and for a small tube a two to five mils plating thickness is suitable. After the cathode 21 is plated, the cathode and mandrel are removed from the form 61 and positioned on the cylindrical projection 54 of the mold 50. The other electrodes are formed in a similar manner, as will be discussed subsequently, and positioned within the mold.

Preferably, leads are positioned on the mandrel followed by plating of the electrode to provide a good structural and electrical connection between the lead and electrode, but may be attached to the electrode after the plating process is complete. It will be appreciated that both the material of the electrode and the material of the leads must have a coefficient of thermal expansion compatable with that of the material from which the neck of the tube is formed. For example, nickel is compatable with certain glass compositions, as well as some alloys of nickel which may be used for leads.

The remaining electrodes 22 through 25 are formed in a similar manner. FIGURE 5 illustrates the manner in which the electrode 22 may be plated on a mandrel 64 which is positioned on a form 65. In this case, the form 65 includes a cylindrical projection 66 extending through a central hole in the mandrel 64. This enables a tool steel arbor 67 as shown in FIGURE 3A to be used for supporting the electrode 22 and mandrel 64 during molding of the tube. The mandrel 64 typically may have a diameter of 0.125 inch, a thickness of 0.010 inch and a length of 0.125 inch for manufacturing a small cathode ray tube. The electrode 22 may be a plating of nickel two to five mils thick, and the mandrel 64 may be machined from aluminum. Again, the form 65 may be made of an acrylic plastic or other suitable material for supporting the mandrel 64 during plating of the electrode 22 and to ensure that only the desired portions of the mandrel 64 are plated.

Each of the electrodes 23 and 25 may consist of a nickel plating on respective mandrels 70 and 71 as shown in FIGURES 6 and 7. The mandrels 70 and 71 may be machined from aluminum, and are positioned on and supported by plastic forms 72 and 73. In a similar manner, the electrode 24 is plated on a machined aluminum mandrel 74 which has a plastic form 75 positioned coaxially therein. For a miniature cathode ray tube, the mandrels 76 and 71 may be approximately 0.125 inch in diameter and 0.018 inch thick, and the mandrel 74 may be 0.125 inch in diameter and 0.250 inch long. In each case, the forms 72, 73 and 75 may be made of an acrylic plastic, and the electrode may have a thickness of two to five mils.

The mandrel 60 having the cathode electrode 21 plated thereon is positioned on the projection 54 as described previously. This is followed by placement of the mandrel 64 and electrode 22 coaxially over the cathode 21. An aluminum spacer 80 is provided between the electrode 22 and the electrode 23 and mandrel 70. In a similar manner, a spacer 81 is provided between the electrode 23 and the electrode 24, which is followed by a spacer 82 and the electrode 25. The electrodes 22 through 25 and their associated mandrels as well as the spacers 30 through 82 are supported and held in position by the tool steel arbor 67. A funnel core 84, which may be made of tool steel or aluminum, is placed on the exterior end of the arbor 67. The free ends of the leads, such as the leads 30, 32 and 36, from the various electrodes are positioned within holes in the mold 50 at the base end of the structure as shown in FIGURE 3A. Molten glass, or other suitable material for the neck and envelope, is poured into the cavities 52 and 51, and the glass is allowed to cool and harden. The completed structure is then removed from the mold 50 and immersed in a solution to dissolve the mandrels. In the case of aluminum mandrels, the completed structure may be immersed in a hot caustic solu tion to dissolve the aluminum, thereby leaving only the plated electrodes and leads permanently secured within the neck of the tube. The neck material essentially forms a bond with the electrode material, and in the case of a glass neck material this bond is similar to a hermetic seal. It will be appreciated that pure nickel has a greater coefficient of thermal expansion than many typical glasses. However, the more impurities included within the glass, the higher its temperature coefficient. It is accordingly desirable that if the neck and envelope are of glass that a glass having a coefiicient as close to that of the electrode material as possible be used. Borosilicate glasses may be used inasmuch as they have a high E factor, that is, they will give or stretch. Additionally, the thickness of the neck with respect to the thickness of the electrodes may be selected to minimize temperature expansion differences. The thickness of an electrode will be in the same direct ratio to the thickness of the neck as the tensile strength of the neck material is to the compressive strength of the electrode material. Alternatively, the portions of the completed electrodes which contact the envelope material may be additionally plated with a different metal having a temperature coefficient closer to that of the material to provide a better expansion coefficient between the electrode wall and the tube material.

The base 15, which may be of glass or a suitable plastie, is secured to the end of the completed neck with the leads being connected with the base pins. Both the base and neck may have a chamfered edge as shown in FIG- URE 2, with a suitable adhesive such as epoxy resin 43 being used to secure the two parts together. The face plate of the tube is applied in a conventional manner, such as by means of dielectric heating or a glass cement. Preferably the base, tube structure and face panel are placed in a vacuum chamber with an electron beam welder being used to secure the parts together, in this manner the tube is evacuated and then molded. Alternatively, a small hole may be formed in the cathode 21 during plating or subsequently to allow evacuation from the base end of the tube after the face plate has been applied. It will be appreciated that the small hole should not be formed in the face of the cathode where the electrons are emitted.

As noted previously, the concepts of the present invention are applicable to the manufacture of various types of electron tubes. This is also true with respect to arrays of cathode ray tube gun and envelope structures coupled with a single face plate or panel to provide a cathode ray tube having a shallow depth, i.e., short between the face panel and base. Devices of this nature in the past have consisted of a plurality of cathode ray tubes having the edges of their envelopes secured together with a single bonded face panel. The manufacture of such tubes can be accomplished by utilizing the concepts of the present invention. Thus, a mold having a plurality of cavities, like cavities 51 and 52 in FIGURE 3A, may be used to accommodate the plural gun structures. The tube and gun structure is formed in the same manner as described above, with the mandrels subsequently being removed. The face panel is then bonded to the periphery of the outer envelopes. A four inch diagonal cathode ray tube having a depth of less than one inch may employ l2 gun structures arranged parallel in a three by four tube array formed in a single mold and coupled with a single face panel. The various guns are operated by means of an electronic switching circuit in a sequential fashion to control the electron beams from the respective guns so as to provide an appropriate scan of the entire face of the tube.

The face panel may have a conventional phosphor applied thereto in a conventional manner prior to bonding to the tube. Additionally, phosphors having different persistances may be applied to the face panel to provide a dual purpose tube for visual indications and photographic recording. A tube of this nature, for example, used to monitor relatively slowly moving wave forms such as those encountered with a cardioscope requires a slow horizontal sweep frequency thereby necessitating the use of a long persistence phosphor, such as P-7 type phosphor which emits a white light visible to the human eye. The long persistence allows the entire trace to be observed with negligible fading of the preceding portion of the trace. However, the light emitted by this phosphor tends to cause a smear in recording on a moving sensitized tape or film. Accordingly, a short persistence phosphor may also be applied along with the long persistence phosphor to the face panel which emits in the response range of the sensitized tape or film. For example, P-l6 phosphor which emits only near ultraviolet light is suitable. The two phosphors may be mixed together and applied to the face panel as a single coating on the panel 11 at prior to bonding the panel to the envelope 10. This combination of the two phosphor coatings enables a dual use of the tube without objectionable interference between the two.

The present embodiments of the invention are to be considered in all respects as illustrative and not restrictive, the scope thereof being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims therefore are intended to be embraced therein.

What is claimed is:

1. A method of forming an electron tube comprising the steps of plating a plurality of metallic electrodes on respective mandrels, positioning the plated electrodes and mandrels within a mold,

applying liquid envelope material into said mold and allowing said material to contact said electrodes and harden thereby securing said electrodes and forming a tube structure,

removing the tube structure from said mold, and

removing said mandrels from said electrodes. 2. A method as in claim 1 including the steps of providing leads coupled with said electrodes prior to positioning said electrodes within said mold, and

coupling said leads to pins in base means after removing said mandrels, and securing said base means to said tube structure.

3. A method as in claim 1 including the steps of bonding a face panel to said tube structure.

4. A method as in claim 1 including the steps of coating 2. face panel with phosphors of different persistences, and

bonding said face panel to said tube structure.

5. A method as in claim 2 including the steps of bonding a face panel to said tube structure.

6. A method as in claim 1 including the steps of providing leads coupled with said electrodes,

positioning groups of plated electrodes and mandrels within respective apertures in a mold, and

securing a face panel to the periphery of said tube structure.

7. A method of forming an electron tube comprising the steps of applying metallic electrodes to respective mandrels,

arranging a plurality of mandrels with applied electrodes on supporting means to form an electrode assembly,

positioning said electrode assembly in an aperture within a mold,

applying envelope material into said aperture within said mold and allowing said material to contact said electrodes therein and harden to provide a bond between said electrodes and said hardened material. to form a tube structure,

removing said supporting means from said mandrels,

removing said tube structure from said mold, and

removing said mandrels from said electrodes.

8. A method as in claim 7 wherein said electrodes are electroplated on respective dissolvable mandrels, and

said mandrels are removed from said electrodes by dissolving said mandrels.

trodes and harden and bond therewith to form a tube structure having an electrode assembly therein, removing said supporting means from said mandrels and removing the tube structure from said mold, and

9. A method as in claim 8 including the steps of removing said mandrels from said electrodes. providing leads coupled with said electrodes prior to 12. A method as in claim 11 wherein positioning said electrodes in said mold, and said material bonds with at least a' peripheral portion securing a face panel to said tube structure. of each of said electrodes. 10. A method as in claim 7 including the steps of 13. A method as in claim 12 including the steps of plating electrodes on a plurality of mandrels, providing leads coupled with said electrodes prior to arranging a plurality of mandrels with plated electrodes positioning said electrodes and mandrels within said thereon on each of a plurality of supporting means mold, and allowing said leads to extend into apertures to form a plurality of electrode assemblies, within said mold to enable said leads to extend expositioning said electrode assemblies in respective aperteriorly of said tube structure, and

tures within a mold, 15 bonding a face panel to said tube structure. applying envelope material into said apertures within 14. A method as in claim 13 including the steps of said mold and allowing said material to contact all coating said face panel with phosphors of different perof said electrodes therein and harden to provide a. sistencies prior to securing said face panel to said bond between said electrodes and said hardened matube structure. terial to form a tube structure having a plurality of References Cited electrode assemblies, and securing a face panel to the periphery of said tube UNITED STATES PATENTS structure 2,082,992 6/1937 Wallace 264-272 11. A method of forming an electron tube comprising 2,423,830 7/1947 FOIlda 31392 h Steps f 2,828,433 3/1958 Frenkel 313-82 positioning a plurality of mandrels on respective forms, 2,856,639 10/1958 Forrest et a1 264 272 plating a metallic electrode on each of said mandrels,

removing said forms from said mandrels,

positioning said plated electrodes and mandrels within a mold on a supporting means with spacing means between at least some of said electrodes,

applying liquid envelope material into said mold and allowing said material to contact each of said elec- JAMES \V. LAWRENCE, Primary Examiner.

V. LAFRANCHI, Assistant Examiner.

US. Cl. X.R. 

1. A METHOD OF FORMING AN ELECTRON TUBE COMPRISING THE STEPS OF PLATING A PLURALITY OF METALLIC ELECTRODES ON RESPECTIVE MANDRELS, POSITIONING THE PLATED ELECTRODES AND MANDRELS WITHIN A MOLD, APPLYING LIQUID ENVELOPE MATERIAL INTO SAID MOLD AND ALLOWING SAID MATERIAL TO CONTACT SAID ELECTRODES AND HARDEN THEREBY SECURING SAID ELECTRODES AND FORMING A TUBE STRUCTURE, REMOVING THE TUBE STRUCTURE FROM SAID MOLD, AND REMOVING SAID MANDRELS FROM SAID ELECTRODES. 